1. Field of the Invention
Rotor blades for wind power installations are known in many different forms. In a wind power installation the rotors or the rotor blades thereof represent the main source of sound. For reasons relating to acceptance and noise prevention laws, the aim should/must be that of minimizing the levels of sound emission as wind power installations are often also set up in the proximity of residential accommodation. The levels of sound emission which hitherto occur with a wind power installation or a wind power converter also mean that wind power installations are faced with resistance from populated areas because of the sound they produce and for that reason such installations can be accepted sometimes with difficulty or not at all as authorities responsible for planning permission refuse permission for wind power installations because of the existing environmental requirements, noise also being an environmentally polluting factor.
2. Description of the Related Art
Many proposals have already been put forward for structurally modifying a rotor blade of a wind power installation in such a way as to afford a reduction in noise. By way of example reference is made here to the documentation as is disclosed in EP-A-0 652 367 or DE 196 14 420.5.
However a reduction in noise by virtue of structural measures on the rotor blade is possible only to a limited extent.
Therefore the object of the invention is further to improve the noise emission of wind power installations.
In accordance with the invention that object is attained by a rotor blade having the features of claim 1. Advantageous developments are set forth in the further claims.
The invention is based on the realization that, if the surface of a rotor blade is at least partially provided with a fluidxe2x80x94and/or ice-repellent layer, the rotor blade also becomes rougher. Therefore, instead of providing the rotor blade with a coating comprising a coat of paint which imparts to the rotor blade on the top thereof a maximum degree of smoothness, it is precisely the opposite that is done, namely it is given a surface which is rough in respect of microstructure. Such surfaces are also known for example from lacquers or coatings which perform the functionality of the so-called xe2x80x9clotus effectxe2x80x9d, so that water/ice adheres only weakly to the surface. In that respect the coating which is produced from a coat of paint comprises a kind of bed of nails of nano size. Those nano-nails of the bed not only roughen up the surface of the rotor blade but also impart a lower level of hardness to the surface because the individual nano-nails are also deformable in their longitudinal direction or are considerably softer in respect of their structure, than the glass fiber coating of a rotor blade.
Thus the xe2x80x9clotusxe2x80x9d coating on the rotor blade provides that the eddies which are formed on the top side of the rotor blade are restrained or checked by the soft structure of the surface or energy is taken from the eddies of air so that overallxe2x80x94as has been notedxe2x80x94the sound which is produced upon rotation of the rotor blade is reduced.
The micro-silicone paint xe2x80x9cLotusanxe2x80x9d (trade mark of ispo GmbH, a company of the Dyckerhoff Group) may be mentioned as a self-cleaning coating or paint with which a considerable reduction in noise of a rotor blade can be achieved in operation. That micro-silicone paint is marketed by the company under the article designation No 1950 and is described as being dirtxe2x80x94and water-repellent. It is also possible for the coating to be formed by a sheet or foil, the surface structure of which forms a water-repellent layer. Self-cleaning surfaces (and the production thereof) are also known from EP 0 772 514.